Bistatic electro-optical device for substance-on-surface chemical recognizer

ABSTRACT

A system for facilitating the measurement of optical parameters of a substance sitting on a surface, so that identification of the substance by reflectance spectroscopy can be made without ambiguity. The system comprises a structure using a bistatic arrangement and an accompanying method to limit, to just two beams, the propagation of light from an arrangement of laser transmitters, via an interposed transparent dielectric, to a receiver thereby preventing multiple reflections within the transparent dielectric from reaching the receiver. The bistatic arrangement comprises laser transmitters and a receiver mounted on a telescoping boom, with both the laser transmitters and receiver being independently orientable, with the positions and orientations of the laser transmitters, the receiver and the telescoping boom electronically sensed at all times.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Utility patent application claims priority benefit of the [U.S. provisional application for patent Ser. No. 62/730,516, entitled “BISTATIC ELECTRO-OPTICAL DEVICE FOR SUBSTANCE-ON-SURFACE CHEMICAL RECOGNIZER”, and filed on 12 Sep. 2018 under 35 U.S.C. 119(e). The contents of this related provisional application are incorporated herein by reference for all purposes to the extent that such subject matter is not inconsistent herewith or limiting hereof.

RELATED CO-PENDING U.S. PATENT APPLICATIONS

Not Applicable.

INCORPORATION BY REFERENCE OF SEQUENCE LISTING PROVIDED AS A TEXT FILE

Not Applicable.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER LISTING APPENDIX

Not applicable.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material that is subject to copyright protection by the author thereof. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure for the purposes of referencing as patent prior art, as it appears in the Patent and Trademark Office, patent file or records, but otherwise reserves all copyright rights whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

FIG. 1 is a rear view of the bistatic sensor system (Bistatic Electro-Optical Device).

FIG. 2 is a side view of the bistatic sensor system and other supporting structures: the view is from the left side of FIG. 1.

FIG. 3 is a view of the aperture and lens contained internally within the receiver module of from the Bistatic Electro-Optical Device. Frequency modulated pencil beams are also shown, but the rest of the apparatus is removed from view.

Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Some embodiments may provide a bistatic electro-optical device for a substance-on-surface chemical recognizer, and a method of using it. In this patent application the phrase “bistatic sensor system” will be used interchangeably with “Bistatic Electro-Optical Device”.

The primary purpose of this present invention is to facilitate the measurement of optical parameters of a substance sitting on a surface, so that identification of the substance by reflectance spectroscopy can be made without ambiguity. Reflectance spectroscopy is a well-established substance identification technique, but in the field it is done presently with monostatic equipment, in which the source of the laser light and the receiver of the returned laser light are co-located. This leads to considerable ambiguity in the determination of the substance's identity. The ambiguity is caused by variations in sample thickness, multiple reflections from the sample and supporting substrate, uncertainty of the interrogatory beam's location, and uncertainty of where the beam is illuminating (sample? Substrate? Or partially sample and partially substrate?).

The apparatus has advantages in identifying the chemical composition of (isotropic and homogeneous) thin liquid and gel films on various surfaces by their infrared reflectance spectra. The bistatic optical sensing device contains a multi-wavelength laser source and a detector which are physically displaced from each other. With the aid of the apparatus, key optical variables can be measured in real time. The variables in question (substance thickness, refractive index, etc.) are those whose unobservability causes many types of monostatic sensor (in use today) to give ambiguous identifications. Knowledge of the aforementioned key optical variables would allow an adaptive signal-processing algorithm to make unambiguous identifications of the unknown chemicals by their infrared spectra, despite their variable presentations. Within the receiver of the apparatus is an aperture that limits the interrogatory beams to a coherent pair, rejecting those resulting from successive multiple reflections. This permits the determination of the necessary optical variables which permit unambiguous identification. One important optical parameter of the substance-to-be-identified is the thickness of the sample. Frequency modulation can produce easily measurable beat frequencies for determination of sample thicknesses on the order of microns to millimeters. Also shown is how the apparatus's polarization features allow it to measure the refractive index of any isotropic, homogeneous dielectric surface on which the unknown substance can sit. Measurement of all of these aforementioned variables facilitate a reduction in ambiguity of substance identification. A monostatic instrument would only be able to rely on the backscatter shown in the FIG. 1 to determine the identity of the unknown substance.

Description and Operation:

The bistatic arrangement of components comprising the Bistatic Electro-Optical Device for a substance-on-surface chemical recognizer instrument is shown in FIG. 1. A side view of the same apparatus is shown in FIG. 2, which also shows additional structures to which support the apparatus of FIG. 1. FIG. 3 shows the arrangement of a lens and adjustable aperture inside the receiver module I. For a list of the various parts illustrated by way of example in the drawings see Table 1 below.

Computer P is connected to A through F and I through L, by means of wires, and also with optical fiber and/or radio links, and can control every aforementioned part to which it is connected, and can read the sensory output of every aforementioned part to which it is connected.

Laser beam D originates within, and is emitted by, transmitter module C, which contains one or more lasers. Laser beam D is composed of multiple co-linear laser beams of different frequencies from infra-red to ultraviolet; said constituent laser beams may be frequency-modulated, amplitude modulated, circularly polarized, linearly polarized, chopped, or a combination of any or all of the aforementioned. The means of modulating, polarizing, or chopping light are prior art, and should be known to anyone skilled in the art. The means of co-locating laser beams along the same line are also prior art, and should be known to anyone skilled in the art.

The frame in FIG. 1 is made up of its constituent parts M, N, O1, O2 and K, in addition to any other connecting framework made obvious by the diagram FIG. 1. The frame supports the optical components and is able to position them.

J1—a motor with angular position encoder—is able to adjust the angular orientation of C and determine the angular position of C. A central computer is able to send positional commands to J1 and read the positional output of J1. Similarly, J2—another motor with angular position encoder—is able to adjust the angular orientation of I and determine the angular position of I. The same central computer that controls and reads J1 is able to send positional commands to J2 and read the positional output of J2. By these means it is possible to orient C and I are so that any beam F that originates from D can be intercepted by I in such a way that the interception is constrained by the laws of refraction and reflection. Telescoping boom K can also be moved linearly in and out of fixed boom N, and this provides an additional means by which I can be positioned to intercept F. Telescoping boom K can be moved by hand or by A, a motor-with-angular-position-encoder. A will move K by means of K having a linear rack of teeth on it, which engage with teeth on the toothed gear mounted on the driveshaft of A.

The purpose of B, the laser profilometer, is to determine the surface profile of the substrate G. The purpose of the camera is to determine what part of the scene the laser beam is illuminating. This eliminates uncertainty as to what is being illuminated by the laser beam, and permits the positions of all movable components to be adjusted so that the sample H is correctly illuminated and so that I can collect any light coming off of the sample H. The camera also permits the positions of all movable components to be adjusted so that the substrate G is correctly illuminated and so that I can collect any light coming off of the substrate G. Together, B and G permit the development of algorithms that use information from the scene to ultimately determine refractive index (of ample and substrate) and also sample thickness.

Determination of the refractive index of the substrate is carried out with the aid of the camera, inertial sensing, and the properties of polarization. With the camera to determine where the bare substrate lies, the placement of the beam accurately on the bare substrate is assured. The profilometer and camera together measure the profile of the surface on which the substance rests. The information from this profile is then used by algorithms to compute refractive index and substance thickness information, which is then used in the substance identification itself. By compensating for ambiguity-inducing changes introduced into a spectrum by the aforementioned variables, the uniqueness of a spectrum can be restored, permitting unambiguous identification.

The diaphragm (or aperture) R is opened to just the right size to accommodate 2 and only 2 beams, and thereby exclude all multiple reflections. This ultimately allows measurement of the spacing between the two beams, and aids in the determination of the thickness of the sample H and also of the refractive index of the sample H. The method of adjusting the size of R is as follows: as the aperture of R is opened gradually from zero width, there will be increasing light intensity on the detector, with zero beat frequency, because only one beam is entering the detector (the primary reflected beam T1). When enough of the cross-section of the 1st emergent beam T2 enters, the detector will then register a beat frequency that is proportional to the sum p=b+na+δ (where δ is a virtually-travelled distance equivalent to the phase change caused by reflection off the bottom interface, b is the path difference between frequency-modulated beams T1 and T2 as shown in FIG. 3, n is the refractive index of the sample H, and a is the distance traversed by the laser light within the sample H, as shown in FIG. 3.). The aperture of R can then narrowed again until the beats disappear, to determine the width of a single beam T1 or T2. The computer P can automatically control the opening and closing of R in real time.

By opening and closing R appropriately, it is possible to measure p, and further calculations can use p to determine d, the sample thickness of H.

Some embodiments may provide a bistatic electro-optical device for a substance-on-surface chemical recognizer (with circular polarization and frequency modulation of the light) and a method of using the device, the purpose of which is to remove the ambiguities that monostatic devices encounter when identifying substances on surfaces. Such embodiments make it possible, to unambiguously identify, in the field, thin liquid or gel films of unknown chemical composition (sitting on unknown surfaces), using wide band infra-red radiation. A solution for doing this is as follows:

(1) Bistatic arrangement of laser transmitter (“TX”) and receiver (“RX”), mounted on a telescoping boom, with both TX and RX independently orientable, with the positions and orientations of (i) TX, (ii) RX and (iii) the telescoping boom electronically sensed at all times.

(2) With the aid of the bistatic arrangement, a structure and accompanying method to limit, to just two beams, the propagation of light from TX (via an interposed transparent dielectric) to RX—thereby preventing multiple reflections within the transparent dielectric from reaching RX.

(3) The laser light is composed of a wide spectrum of frequencies, visible and infra-red, the infrared achieved by several quantum cascade lasers and the visible by several colors of light: these light sources can be frequency-modulated at will. The frequency modulation enables distances to be measured, and hence the thickness of the thin film to be identified. You are going to have to refer to my attached provisional patent application and my published paper because there is no way I can do it justice in the constrained context of this answer field (Fauconier, R., Ndoye, M. and Montlouis, W., “Optical fundamentals of an adaptive substance-on-surface chemical recognizer”, SPIE Security and Defence 2017 Proceedings, Volume 10433, No. 3, Electro-Optical and Infrared Systems: Technology and Applications XIV, Warsaw, Poland, September 2017).

(4) The fact that the laser light is composed of multiple frequencies allows distance measurements to be made at frequencies which are not absorbed by the substance.

(5) Since the laser light is circularly polarized, and since there is a camera in the apparatus, the arrangement can be automatically moved to sample bare surfaces to compute the refractive index of the supporting surface by Fresnel's equations.

(6) The arrangement allows the refractive index and thickness of the interrogated film to be determined, by the equations in my paper.

(7) A laser profilometer also aids in determining the shape of the surface on which the interrogated thin film rests, which aids in the calculations.

Distinguishing features: (1) Bistatic arrangement of laser transmitter (“TX”) and receiver (“RX”), mounted on a telescoping boom, with both TX and RX independently orientable, with the positions and orientations of (i) TX, (ii) RX and (iii) the telescoping boom electronically sensed at all times. (2) With the aid of the bistatic arrangement, a structure and accompanying method to limit, to just two beams, the propagation of light from TX (via an interposed transparent dielectric) to RX—thereby preventing multiple reflections within the transparent dielectric from reaching RX.

Analogous art would be bistatic radars, but these are presently not generally set up to determine the parameters that my device is set up to determine. A bistatic radar that were set up totally analogously to my electro-optical device should be able to determine atmospheric parameters between TX and RX, or ground parameters between TX and RX, which would help in military radars, weather radars and ground-penetrating radars that identify IEDs (improvised explosive devices) and other buried objects.

The new capabilities which are not even contemplated by existing approaches are

(1) the ability to measure the thickness of a transparent dielectric film, sitting free on any surface, with no prior preparation of the film, no contact with or handling of the film and no foreknowledge whatsoever of the film's chemical makeup

(2) the ability to measure the refractive index of a transparent dielectric film, sitting free on any surface, with no prior preparation of the film, no contact with or handling of the film and no foreknowledge whatsoever of the film's chemical makeup

(3) as a result of (1) and (2) and accompanying algorithms, the capability to eliminate film thickness and refractive index as ambiguity contributors, in the stand-off identification of chemical substances on surfaces.

LIST OF THE VARIOUS PARTS OF THE DRAWINGS

TABLE 1 List of significant parts of the invention and also of other things relevant to its use. Alphanumeric Designation Description of Drawing Part A Motor with angular position encoder (drives telescoping boom) B Laser profilometer (e.g. Keyence LJ-G030) C Transmitter module (visible & mid-infrared laser source) D Laser beam emitted by C E Backscattered light from G F The beam that results from the following: (i) That part of D which reflects off of H (ii) That part of D which is refracted by H and reflected off of G G Substrate H Chemical sample for analysis I Receiver module J1 Motor with angular position encoder J2 Motor with angular position encoder K Telescoping boom L Auxiliary camera M Handle N Fixed boom O1 Fork that supports C, and in which C is free to pivot O2 Fork that supports I, and in which I is free to pivot P Laptop or other computer Q Lens (inside of I) R Adjustable diaphragm or aperture (inside of I) T1 Pencil beam of light that enters I after reflection off the top surface of H T2 Pencil beam of light that enters I after reflection off the interface between G and H 

What is claimed is:
 1. A Device comprising: A bistatic arrangement of laser transmitters and a receiver, mounted on a telescoping boom, with both said arrangement of laser transmitters and said receiver being independently orientable, with the positions and orientations of said arrangement of laser transmitters, said receiver and said telescoping boom electronically sensed at all times.
 2. A System for facilitating the measurement of optical parameters of a substance sitting on a surface, so that identification of said substance by reflectance spectroscopy can be made without ambiguity.
 3. The System of claim 2 comprising: a structure using a bistatic arrangement and an accompanying method to limit, to just two beams, the propagation of light from an arrangement of laser transmitters, via an interposed transparent dielectric, to a receiver thereby preventing multiple reflections within said transparent dielectric from reaching said receiver.
 4. The System of claim 2 further comprising: the ability to measure the thickness of a transparent dielectric film, sitting free on any surface, with no prior preparation of the film, no contact with or handling of the film and no foreknowledge whatsoever of the film's chemical makeup; the ability to measure the refractive index of a transparent dielectric film, sitting free on any surface, with no prior preparation of the film, no contact with or handling of the film and no foreknowledge whatsoever of the film's chemical makeup; and the capability to eliminate film thickness and refractive index as ambiguity contributors, in the stand-off identification of chemical substances on surfaces. 